This invention relates to an interface circuit for the transmission of digital data between digital data handling systems operating with different clock frequencies.
Known asynchronous interface circuits such as USARTs (Universal Synchronous/Asynchronous Receiver/Transmitter) serve for communication between microprocessors and serial input/output units. Here parallel data has to be transformed into serial data, and serial data into parallel data. For the asynchronous transmission of serial data there are transmitted, in addition to the data bits of a message, synchronising start and stop bits. The transmission speed of USARTs in digital data processing systems is relatively low. Data of faster systems, e.g. data of a pulse code modulated video signal, cannot be processed or transmitted by a USART.